/*
 * jdtrans.c
 *
 * Copyright (C) 1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains library routines for transcoding decompression,
 * that is, reading raw DCT coefficient arrays from an input JPEG file.
 * The routines in jdapimin.c will also be needed by a transcoder.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* Forward declarations */
LOCAL void transdecode_master_selection JPP((j_decompress_ptr cinfo));


/*
 * Read the coefficient arrays from a JPEG file.
 * jpeg_read_header must be completed before calling this.
 *
 * The entire image is read into a set of virtual coefficient-block arrays,
 * one per component.  The return value is a pointer to the array of
 * virtual-array descriptors.  These can be manipulated directly via the
 * JPEG memory manager, or handed off to jpeg_write_coefficients().
 * To release the memory occupied by the virtual arrays, call
 * jpeg_finish_decompress() when done with the data.
 *
 * Returns NULL if suspended.  This case need be checked only if
 * a suspending data source is used.
 */

GLOBAL jvirt_barray_ptr *jpeg_read_coefficients(j_decompress_ptr cinfo)
{
	if(cinfo->global_state == DSTATE_READY)
	{
		/* First call: initialize active modules */
		transdecode_master_selection(cinfo);
		cinfo->global_state = DSTATE_RDCOEFS;
	}
	else if(cinfo->global_state != DSTATE_RDCOEFS)
		ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
	/* Absorb whole file into the coef buffer */
	for(;;)
	{
		int             retcode;

		/* Call progress monitor hook if present */
		if(cinfo->progress != NULL)
			(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
		/* Absorb some more input */
		retcode = (*cinfo->inputctl->consume_input) (cinfo);
		if(retcode == JPEG_SUSPENDED)
			return NULL;
		if(retcode == JPEG_REACHED_EOI)
			break;
		/* Advance progress counter if appropriate */
		if(cinfo->progress != NULL && (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS))
		{
			if(++cinfo->progress->pass_counter >= cinfo->progress->pass_limit)
			{
				/* startup underestimated number of scans; ratchet up one scan */
				cinfo->progress->pass_limit += (long)cinfo->total_iMCU_rows;
			}
		}
	}
	/* Set state so that jpeg_finish_decompress does the right thing */
	cinfo->global_state = DSTATE_STOPPING;
	return cinfo->coef->coef_arrays;
}


/*
 * Master selection of decompression modules for transcoding.
 * This substitutes for jdmaster.c's initialization of the full decompressor.
 */

LOCAL void transdecode_master_selection(j_decompress_ptr cinfo)
{
	/* Entropy decoding: either Huffman or arithmetic coding. */
	if(cinfo->arith_code)
	{
		ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
	}
	else
	{
		if(cinfo->progressive_mode)
		{
#ifdef D_PROGRESSIVE_SUPPORTED
			jinit_phuff_decoder(cinfo);
#else
			ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
		}
		else
			jinit_huff_decoder(cinfo);
	}

	/* Always get a full-image coefficient buffer. */
	jinit_d_coef_controller(cinfo, TRUE);

	/* We can now tell the memory manager to allocate virtual arrays. */
	(*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);

	/* Initialize input side of decompressor to consume first scan. */
	(*cinfo->inputctl->start_input_pass) (cinfo);

	/* Initialize progress monitoring. */
	if(cinfo->progress != NULL)
	{
		int             nscans;

		/* Estimate number of scans to set pass_limit. */
		if(cinfo->progressive_mode)
		{
			/* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
			nscans = 2 + 3 * cinfo->num_components;
		}
		else if(cinfo->inputctl->has_multiple_scans)
		{
			/* For a nonprogressive multiscan file, estimate 1 scan per component. */
			nscans = cinfo->num_components;
		}
		else
		{
			nscans = 1;
		}
		cinfo->progress->pass_counter = 0L;
		cinfo->progress->pass_limit = (long)cinfo->total_iMCU_rows * nscans;
		cinfo->progress->completed_passes = 0;
		cinfo->progress->total_passes = 1;
	}
}
